Immune System: Innate and Adaptive Immunity Explained


Our body has a powerful army that protects it from various types of threats. These threats can come in the form of mechanical injuries, the entry of germs, or the entry of other foreign particles like dust. This personal army is called the immune system. Every day, we encounter a huge number of bacteria, viruses and other disease-causing organisms. However, we don’t fall ill every other day. which is due to our immune system – an army of cells that is always roaming our body, ready to ward off any attack. The immune system can be broadly divided into
two parts – innate and adaptive immunity. Innate immunity or non-specific immunity is
the body’s first natural defense to any intruder. This system doesn’t care what it’s killing. Its primary goal is to prevent any intruder
from entering the body, and if it does enter, then the immune system kills this intruder. It doesn’t differentiate between one pathogen
and another. The first component of this defensive system
is your skin. Any organism trying to get into the body is
stopped by the skin, our largest organ, which covers us. Secondly, there is the mucous lining of all
our organs. The sticky, viscous fluid of this lining traps
any pathogens trying to get past it. These are the physical barriers. However, we also have chemical barriers, such
as the lysozyme in the eyes, or the acid in the stomach, which kill pathogens trying to
gain entry. The genitourinary tract and other places have
their own normal flora, or microbial community. These compete with pathogens for space and
food, and therefore also act as a barrier. The next line of defense is inflammation,
which is done by mast cells. These cells are constantly searching for suspicious
objects in the body. When they find something, they release a signal
in the form of histamine molecules. These alert the body, and blood is rushed
to the problem area. This causes inflammation and also brings leukocytes,
or white blood cells, which are soldiers in our body’s cellular army. Once they come, all hell breaks loose! Sometimes however, the intruder may not be
germ, but rather a harmless thing like a dust particle. The body still causes a full immune reaction to this intruder, which is how allergic reactions occur. In the fortress of our body, the leukocytes
are VIPs. They have an all-access pass to the body,
except, of course, to the brain and spinal cord. Our leukocytes come in many types. Those that belong to the innate system are the phagocytes. These cells can either patrol your body, like the neutrophils, or they can stay in certain places and wait for their cue. Neutrophils are the most abundant cells. They patrol the body and can therefore get
to a breach site very quickly. These cellular soldiers kill the infectious
cell and then die, which leads to pus formation. There are also the big bad wolves, or the
macrophages. These cells are like hungry, ravenous monsters
who simply engulf unwanted pathogens. Instead of roaming freely in our blood, they
are collected in certain places. These cells can consume about 100 pathogens
before they die, but they can also detect our own cells that have gone rogue, such as
cancer cells, and kill them too. Beyond that, we also have the Natural Killer
Cells. These cells can efficiently detect when our
own cells have gone rogue, or are infected with, say, a virus. NKCs detect a protein produced by normal cells,
called the Major Histocompatibility Complex or MHC. Basically, whenever a cell isn’t normal, it
stops producing this protein. The NKCs move around constantly, checking
our cells for this type of deficiency, and when they find an abnormal cell, they simply
bind to it and release chemicals that will destroy it. The last cells of our innate immune system
are the dendritic cells. These are found in places that come in contact
with the outside environment, such as the nose, lungs, etc. They are the link between our innate and adaptive immune systems. They eat a pathogen, and then carry information about it to our adaptive immune system cells. This information is produced and shared in
the form of antigens. Antigens are the traces that pathogens leave
around. They are molecules found on the surface on
pathogens that can be detected by our adaptive immune system for recognition. The dendritic cells pass on this information
to our T cells. However, macrophages can also perform this
function. Now, there is also the adaptive or acquired
immune system. This system is more efficient, as it can differentiate
between different types of pathogens. It has 2 main components – T lymphocytes and
B lymphocytes. T-cells come into play when an infection has
already occurred, thus bringing about the cell-mediated immune response. B-cells join the fight when the pathogens
have entered, but haven’t yet caused any disease. This is called the humoral immune response. Some T-cells take signals from the dendritic
cells or macrophages, and are thus called helper T-cells. They perform two key tasks: forming effector
T-cells, which are basically cells that cycle through the body and call in the cavalry,
namely other white blood cells. Helper T-cells also form memory T-cells, which
keep a record of this antigen for future reference. Sometimes, the some cells of our body know
that they have lost the battle. Essentially, the affected area or organ has
They have become heavily infected with pathogens, so there is no hope for them. At this point, the immune system brings out
the cytotoxic t cells. These cells rush over and perform a mercy
killing for the infected and dying cell. Furthermore, we have the B-cells. They produce chemicals called antibodies,
which fit on the antigens of pathogens, much like how a lock and key fit together. These antibodies crowd around a pathogen and
act like tags. They signal the macrophages to come and kill
the marked pathogen. B-cells also produce memory B-cells when they
encounter an antigen. The B- and T- memory cells jointly maintain
a record of all encountered infections, and thus strengthen and solidify the body’s
immune response to these infections. Our innate immune response is quicker, though
non-specific. It gets into action within hours and is pretty
strong. However, when things get out of hand, the
innate system calls for help from the acquired immune system. This system can take days to mount a response,
but the next time we encounter that pathogen, it won’t make us get sick. In short, every day that we spend being healthy is all thanks to our immune system. So, it definitely deserves our respect.

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